TimeTree Puts an Evolutionary Family Tree of Life's Diversity at Your Fingertips

Two years before he published The Origin of Species, Charles Darwin wrote a letter to his friend Thomas Henry Huxley in which he predicted, "The time will come, I believe, though I shall not live to see it, where we shall have fairly true genealogical trees of each great kingdom of Nature."

Thanks to a decades-long revolution in DNA sequencing and data analysis, Darwin’s dream is becoming true. A team of researchers at the Center for Biodiversity at Temple University has released the latest and greatest version of TimeTree, an interactive visualization of the history of life on Earth.

Visitors to TimeTree.org can use the upgraded search engine to see precisely when two different species diverged in time, to trace the full evolutionary timeline of a single species, or to create a many-branched “family tree” for an entire class or kingdom of plants or animals.

When did humans and cats diverge? Only 94 million years ago. Humans and carrots, meanwhile, went our separate ways around 1.5 billion years ago. (That still doesn’t explain Carrot Top.)

“It’s the history of Earth, right there at people’s fingertips,” said Blair Hedges, director of the Center for Biodiversity and co-creator of TimeTree with his Temple University colleague Sudhir Kumar.

This new version of the TimeTree web, a substantial update to the original created in 2009, not only includes colorful and clear visualizations of the divergence of different species across time, but also charts the atmospheric conditions and other “abiological” events that may have influenced the formation of new species.

“Oxygen levels, solar radiation, asteroid impacts — evolutionary biologists for years have looked at how the environment has affected life through time," Hedges told Seeker. "Here we have it all laid out."

One interesting example is the spike in oxygen levels that occurred during the Paleozoic era. That hyper-oxygenated air is believed to be responsible for the huge insects that roamed the Earth, like dragonflies the size of seagulls.

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If you go to the TimeTree web and search for “insecta” in the field that says “Build a TimeTree,” you can make an interesting correlation. As oxygen levels crested over the course of 150 million years, you see a related cluster of divergences over the same time period that created entire new orders of insects. After the oxygen spike flattened out about 200 million years ago, no new orders were born.

Not all environmental correlations are so easy. For example, biologists expected to see a big branching out of mammals after the Chicxulub asteroid impact that wiped out the dinosaurs 65 million years ago. But aside from elephants, manatees, koalas and some moles — all of which diverged soon after the event — most mammal appear to have evolved over the 100 million-year period before the asteroid crashed to Earth.

“These small mammals were scurrying under the feet of dinosaurs,” Hedges said.

The TimeTree engine is built upon a database of evolutionary data collected from 3,000 published research studies covering 97,000 species. The science behind the timeline is something called a “molecular clock.” Researchers count the number of mutations that accumulate on a DNA sequence over time.

Even though mutations occur randomly, Hedges explained, “they generate a constant relationship with time.” Like the constant decay rate of isotopes that we use to date rocks and fossils.

“We obtain a rate of change from the DNA data by measuring the amount of mutations separating two species with a known time of divergence, which we get from the fossil record,” said Hedges. “Then we use that same rate of change to date the splits between other species on the tree.”

He sees a wide audience for the new and improved TimeTree, including teachers who can use the tool to visualize Darwin’s world-changing ideas in action.

“Obviously scientists can really get into the TimeTree and find out all kinds of detailed information,” Hedges remarked. “If you’re not a scientist, and you’re sitting in a bar with friends, and you want to know how far away you are from a gorilla, now you’ve got the answer.”

Nine million years, by the way.

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